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/*
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* Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "rdtsc_x86.hpp"
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#include "runtime/thread.inline.hpp"
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#include "vm_version_ext_x86.hpp"
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// The following header contains the implementations of rdtsc()
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#include OS_CPU_HEADER_INLINE(os)
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static jlong _epoch = 0;
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static bool rdtsc_elapsed_counter_enabled = false;
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static jlong tsc_frequency = 0;
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static jlong set_epoch() {
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assert(0 == _epoch, "invariant");
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_epoch = os::rdtsc();
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return _epoch;
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}
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// Base loop to estimate ticks frequency for tsc counter from user mode.
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// Volatiles and sleep() are used to prevent compiler from applying optimizations.
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static void do_time_measurements(volatile jlong& time_base,
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volatile jlong& time_fast,
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volatile jlong& time_base_elapsed,
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volatile jlong& time_fast_elapsed) {
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static const unsigned int FT_SLEEP_MILLISECS = 1;
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const unsigned int loopcount = 3;
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volatile jlong start = 0;
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volatile jlong fstart = 0;
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volatile jlong end = 0;
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volatile jlong fend = 0;
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// Figure out the difference between rdtsc and os provided timer.
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// base algorithm adopted from JRockit.
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for (unsigned int times = 0; times < loopcount; times++) {
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start = os::elapsed_counter();
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OrderAccess::fence();
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fstart = os::rdtsc();
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// use sleep to prevent compiler from optimizing
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os::sleep(Thread::current(), FT_SLEEP_MILLISECS, true);
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end = os::elapsed_counter();
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OrderAccess::fence();
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fend = os::rdtsc();
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time_base += end - start;
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time_fast += fend - fstart;
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// basis for calculating the os tick start
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// to fast time tick start offset
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time_base_elapsed += end;
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time_fast_elapsed += (fend - _epoch);
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}
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time_base /= loopcount;
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time_fast /= loopcount;
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time_base_elapsed /= loopcount;
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time_fast_elapsed /= loopcount;
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}
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static jlong initialize_frequency() {
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assert(0 == tsc_frequency, "invariant");
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assert(0 == _epoch, "invariant");
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const jlong initial_counter = set_epoch();
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if (initial_counter == 0) {
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return 0;
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}
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// os time frequency
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static double os_freq = (double)os::elapsed_frequency();
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assert(os_freq > 0, "os_elapsed frequency corruption!");
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double tsc_freq = .0;
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double os_to_tsc_conv_factor = 1.0;
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// if platform supports invariant tsc,
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// apply higher resolution and granularity for conversion calculations
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if (VM_Version_Ext::supports_tscinv_ext()) {
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// for invariant tsc platforms, take the maximum qualified cpu frequency
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tsc_freq = (double)VM_Version_Ext::maximum_qualified_cpu_frequency();
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os_to_tsc_conv_factor = tsc_freq / os_freq;
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} else {
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// use measurements to estimate
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// a conversion factor and the tsc frequency
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volatile jlong time_base = 0;
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volatile jlong time_fast = 0;
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volatile jlong time_base_elapsed = 0;
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volatile jlong time_fast_elapsed = 0;
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// do measurements to get base data
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// on os timer and fast ticks tsc time relation.
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do_time_measurements(time_base, time_fast, time_base_elapsed, time_fast_elapsed);
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// if invalid measurements, cannot proceed
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if (time_fast == 0 || time_base == 0) {
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return 0;
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}
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os_to_tsc_conv_factor = (double)time_fast / (double)time_base;
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if (os_to_tsc_conv_factor > 1) {
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// estimate on tsc counter frequency
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tsc_freq = os_to_tsc_conv_factor * os_freq;
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}
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}
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if ((tsc_freq < 0) || (tsc_freq > 0 && tsc_freq <= os_freq) || (os_to_tsc_conv_factor <= 1)) {
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// safer to run with normal os time
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tsc_freq = .0;
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}
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// frequency of the tsc_counter
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return (jlong)tsc_freq;
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}
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static bool initialize_elapsed_counter() {
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tsc_frequency = initialize_frequency();
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return tsc_frequency != 0 && _epoch != 0;
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}
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static bool ergonomics() {
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const bool invtsc_support = Rdtsc::is_supported();
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if (FLAG_IS_DEFAULT(UseFastUnorderedTimeStamps) && invtsc_support) {
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FLAG_SET_ERGO(bool, UseFastUnorderedTimeStamps, true);
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}
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bool ft_enabled = UseFastUnorderedTimeStamps && invtsc_support;
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if (!ft_enabled) {
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if (UseFastUnorderedTimeStamps && VM_Version::supports_tsc()) {
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warning("\nThe hardware does not support invariant tsc (INVTSC) register and/or cannot guarantee tsc synchronization between sockets at startup.\n"\
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"Values returned via rdtsc() are not guaranteed to be accurate, esp. when comparing values from cross sockets reads. Enabling UseFastUnorderedTimeStamps on non-invariant tsc hardware should be considered experimental.\n");
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ft_enabled = true;
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}
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}
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if (!ft_enabled) {
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// Warn if unable to support command-line flag
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if (UseFastUnorderedTimeStamps && !VM_Version::supports_tsc()) {
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warning("Ignoring UseFastUnorderedTimeStamps, hardware does not support normal tsc");
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}
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}
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return ft_enabled;
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}
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bool Rdtsc::is_supported() {
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return VM_Version_Ext::supports_tscinv_ext();
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}
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bool Rdtsc::is_elapsed_counter_enabled() {
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return rdtsc_elapsed_counter_enabled;
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}
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jlong Rdtsc::frequency() {
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return tsc_frequency;
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}
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jlong Rdtsc::elapsed_counter() {
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return os::rdtsc() - _epoch;
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}
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jlong Rdtsc::epoch() {
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return _epoch;
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}
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jlong Rdtsc::raw() {
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return os::rdtsc();
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}
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bool Rdtsc::initialize() {
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static bool initialized = false;
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if (!initialized) {
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assert(!rdtsc_elapsed_counter_enabled, "invariant");
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VM_Version_Ext::initialize();
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assert(0 == tsc_frequency, "invariant");
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assert(0 == _epoch, "invariant");
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bool result = initialize_elapsed_counter(); // init hw
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if (result) {
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result = ergonomics(); // check logical state
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}
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rdtsc_elapsed_counter_enabled = result;
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initialized = true;
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}
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return rdtsc_elapsed_counter_enabled;
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}
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